Normally, in the field of electrophotographic copying process, a corona discharge device is widely used as a device for uniform electric charging of a photoreceptor drum or a device for transferring a toner image formed on a photoreceptor drum to a belt or paper.
In a corotron or a scorotron as the corona discharge device, a corona discharge is performed in the air. Therefore, ozone and nitrogen oxide are generated by a reaction of an oxygen molecule with an active particle of oxygen or nitrogen generated by a non-elastic collision between an electrically charged particle and an oxygen molecule or a nitrogen molecule, the electrically charged particle being accelerated in a discharging field. An exhaust fan provided in an electrophotographic copier releases air containing ozone and the like to the outside. However, ozone is a gas which has a strong odor. Ozone is harmful to human because it may cause physiologic effects such as short breath, dizziness, headache, and nausea when a person is exposed to an air at about 0.1 ppm ozone concentration.
Further, ozone and nitrogen oxide generated by a corona discharge device are adhered to a surface of a photoreceptor drum provided opposing to the corona discharge device and then absorb moisture under a highly humid condition. This reduces a surface resistance of the photoreceptor drum, thereby resulting in image deficiencies such as a fog of a toner image. Further, ozone has a strong chemical action so that it is difficult to maintain a stable electric charge supply when a chemical reaction progresses between ozone and various types of photoreceptors such as an organic photoreceptor.
Therefore, a corona discharge device has been widely used conventionally, which can remove discharge products (products produced in the discharging) such as ozone and nitrogen oxide, from the air to be released from an electrophotographic copier to the outside and which can prevent of the contamination to a photoreceptor.
For example, in a corona discharge device 100 disclosed in a patent document 1, a shield member 101 has a discharge product removing material such as manganous oxide on its surface as illustrated in FIG. 15 (a), FIG. 15 (b), and FIG. 15 (c).
The shield member 101 has a shape of long and narrow box that is open on one side and has a cross-section that looks like a U shape. Inside the shield member 101, insulating blocks 102 and 103 are provided and a wire 104 as a discharge electrode is extended between the insulating blocks 102 and 103. The shield member 101 is made of a paper material 107 in which a flat paper board 105 is coated with a conductive sheet 106, the paper material 107 being bent in the shape.
The conductive sheet 106 is a sheet, for example, an activated carbon sheet, or a metal sheet coated with a metal such as nickel or aluminum by plating or deposition. Note that the activated carbon sheet includes noble metals such as manganous oxide, titanic oxide, Pt, Pd, and Ru.
Therefore, when discharge products such as ozone and titanic oxide, which were generated around the wire 104 during an electric discharge, arrive at a surface of the shield member 101, the discharge products contact and react with the discharge product removing material. As a result, ozone and nitrogen oxide change into an oxygen molecule and nitric acid respectively, thereby becoming collectable.
Further, in a corona discharge device 200 disclosed in a patent document 2, a shield member 201 internally has, i.e. inside a corona discharging field, a discharge product removing member 202 on which manganous oxide or the like is provided, as illustrated in FIG. 16, FIG. 17 (a), and FIG. 17 (b).
The discharge product removing member 202 has a lot of through-holes 203. Therefore, the through-holes 203 allow ion stream to pass therethrough. In other words, the discharge products in the ion wind refluxing inside the shield member 201 are collected inside the discharge product removing member 202.
Further, instead of using the ion wind refluxing inside the shield member 201, it is possible to collect discharge products by forcibly aspirating air with use of an exhaust air duct 204 and an exhaust fan 205, which are provided at the back of the discharge product removing member 202.
Patent Document 1: Japanese Unexamined Patent Application, Tokukaihei, 2-259673 (date of publication: Oct. 22, 1990)
Patent Document 2: Japanese Unexamined Patent Application, Tokukaihei, 6-317974 (date of publication: Nov. 15, 1994)